deleted system folder and can't reboot with itunes because it's password protected

i was just goofing around with my iphone3gs and i "accidentaly deleted the system folder and now i can't use it because everytime i open it it just stays in the apple logo i tried using itunes to reboot but itunes can't access it because it is password protected.....

does anyone know how to fix this?? please the phone has a sentimental value to me..:(

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